Prime Numbers

Sieve of EratosthenesPrime Number Trick
Using prime numbers, you can amaze your friends with a prime prediction...

• Ask your friends to pick any prime number bigger than 5, but they must not tell you what it is.
• Square it. (In other words multiply the prime number by itself.)
• Add 17
• Divide by 12

Without knowing which prime number your friends picked, you can still tell them:

There will be a remainder of 6.

(Or if they do the sum on a calculator, the answer will end with " .5")